Plasma booster for plasma treatment installation

ABSTRACT

An arrangement for boosting or igniting a glow discharge plasma for coating workpieces has at least one hollow body of an electrically conductive material formed such that when an electric signal is applied to the hollow body at least in a certain pressure and voltage range, the geometric conditions for the ignition of a discharge in the interior of the hollow body are satisfied. The hollow body has at least one opening through which charge carriers can flow off into the environs of the arrangement in order to ignite and operate the plasma or to boost a plasma existing there. The arrangement has a mechanism which connects the hollow body electrically with the workpieces such that the hollow body is essentially at workpiece potential.

FIELD OF TECHNOLOGY

The invention relates to a plasma booster for a plasma treatmentinstallation according to the preamble of claim 1, in particular for usein a vacuum coating installation according to claim 15 and for a vacuumtreatment method according to claim 18 respectively.

PRIOR ART

Hot or cold cathodes are known, in which by applying a voltage between acathode, for example a spiral-wound filament or a point with highnegative potential, and an anode, electrons are extracted into thetreatment space of a vacuum coating installation in order to increasethe density of the charge carriers at that site. Such electron sourcesor ion sources are provided with their own electrical supply. Thecathode is conventionally only connected with the treatment space of theplasma treatment installation via a screen in order to avoid loading ofthe cathode through reactive gas or other negative effects due to theplasma treatment process. Of disadvantage is, on the one hand, that theelectrons are generated outside of the coating chamber and consequentlyfurther devices are necessary to transfer them into the treatmentchamber with as few losses as possible. On the other hand, due to theadditionally necessary electrical supply and complex structuring, forreasons of costs alone, only a small number of such electron or ionsources can be provided. Most often, if at all, only one such ionsources is provided with a plasma treatment installation.

Known methods for the deposition of DLC layers, i.e. layers with a highcomponent of sp³ carbon bonds, such as described for example in WO01/79585, utilize an intermediate frequency excitation on the substratein order to generate a layer deposition through the developing glowdischarge. The glow discharge is generated between the parts and theinstallation wall by means of a DC or by means of a unipolar or bipolarpulsed substrate bias in the pressure range of conventional magnetronsputter deposition.

The pieces to be coated are therein actively included in the process.The achievable deposition rate is thereby inter alia strongly determinedby the geometry of the configuration with respect to the workpiececoating in the coating installation, which causes strong fluctuations inthe deposition rate. The condition may thereby arise that weakionization is generated with a less active configuration. This leads toa low deposition rate and therewith to low productivity.

In known plasma treatment installations workpieces are held on substratecarriers, for example in the form of a carousel and guided past thecoating source(s). Examples thereof are doubly rotating configurationswith geometric distances outside the range of 20-80 mm, whereby nocontrolled hollow-cathode plasma is generated. Typical problem areas arethe coating of plate configurations and flat parts, which generate onlya low plasma stream.

In general an increase of the carbon supply by increasing the reactivegas flow is only possible to a limited extent through the throughput ofthe vacuum pumping system, since the layer quality is compromised whenleaving the optimal process window.

DESCRIPTION OF THE INVENTION

The invention is based on the task of providing a plasma booster whichcan be installed into the plasma treatment space or directly onto acarousel or even integrated in a workpiece carrier without elaborate andcostly additional measures.

This task is solved through the inventive characteristics in thecharacterizing clause of claim 1. The plasma booster can therein beoperated through a bias supply to impress an electric signal onto theworkpieces.

Of the conventional plasma processes is known that, depending on theprocess pressure and the applied voltage, through specific geometricconfigurations one or several secondary plasmas may be generated throughthe so-called hollow-cathode effect. While having a locally restrictedyet very high density, these secondary plasmas interfere with theplanned plasma process through different effects such as overheating ofindividual substrates, plasma fluctuations, graphitization in the gasphase and others. For that reason in all conventional Plasma CVD methodsprecautions must be taken in order to avoid such secondary plasmas.

Through an arrangement implemented according to the invention it wasunexpectedly achieved to utilize the hollow-cathode effect withoutdamaging consequences onto process management or layer quality through aplasma booster with an empirically determinable geometry depending onthe process parameters, such that a stable augmentation of the plasmadensity and a significant increase of the deposition rate becomespossible.

The arrangement according to the invention for augmenting and/origniting a glow discharge plasma comprises at least one hollow body ofan electrically conductive material, the hollow space of the hollow bodybeing implemented such that when an electric signal is impressed on thehollow body, at least in a certain pressure and voltage range thegeometric conditions for the ignition of a discharge in the interior ofthe hollow body are satisfied. The hollow body comprises furthermore atleast one opening through which the charge carriers can flow off intothe environs of the arrangement in order to permit there the ignitionand operation of a plasma or to boost a plasma existing there.

The geometry is here selected such that the process temperature can bekept low to avoid affecting the properties of the workpieces. Criticalfor the geometry of the plasma booster substantially encompassing atleast one hollow space are here the inner dimensions or a characteristicgeometric parameter of the hollow space which represents acharacteristic number for the mean distance of the areas of equalelectric potential encompassing the hollow space. For example for apressure range of 1×10⁻³ mbar to 5×10⁻² mbar, preferably 4×10⁻³ mbar to2−10 ⁻² mbar a mean distance range of 20 to 200 mm, preferably 60 to 100mm has been found to be suitable.

The application of this principle can take place thereby that at leastone arrangement according to the invention is installed as a plasmabooster into the loading of a carousel with workpiece carriers, wherebythe plasma density is increased in the entire treatment space and, forexample, a higher deposition rate can be attained.

Alternatively, the workpieces can be fastened directly on an arrangementaccording to the invention and therewith come directly into connectionwith the plasma of the hollow cathode. Combinations of variousembodiments of the arrangement according to the invention can be also beutilized advantageously.

In the following an attempt is made to explain the phenomena underlyingthe invention by means of known laws of physics. However, this can onlybe seen as a, possibly flawed, approximation to the relationshipsobtaining in an industrial coating installation. These [relationships]may differ significantly from the models developed by means ofexemplifying simplified assumptions, for example with respect to thecomplex geometries occurring or moved electrodes.

Under the assumption that an arrangement according to the invention forboosting the plasma, which is comprised either of one or several plasmabooster trees or of substrate trees of corresponding geometry, theyrepresent a cathode for a glow discharge, the anode being the coatingchamber which is preferably at ground potential. For the ignition of theglow discharge a voltage is applied between anode and cathode which isbetween 200 V and 2000 V, preferably between 400 V and 1200 V, eachincluding the limit values. After the ignition the discharge can also beoperated at a lower voltage.

The ignition of the plasma follows Paschen's law. According to this lawthe ignition voltage V_(t), or the ignition potential E_(t) is afunction of the type of gas and at a given type of gas is a function ofthe product of electrode distance d and pressure p:V ₁ =[B×p×d ]/[C+ln pd], E _(t) =B /[C+ln pd];where B and C are gas type-dependent constants.

As is known to a person of skill in the art, there are different optionsfor improving the ignition process. For example when applying a DCvoltage, it can be briefly pulsed at high frequencies. Independently ofthe type of operator voltage, which may be a DC, a bipolar or unipolarpulse, a conventional AC voltage or also a modulated DC voltage, theignition of a plasma booster according to the invention can be affectedor improved through the following measures:

-   -   rapid pressure fluctuations,    -   brief voltage increase (single voltage pulse),    -   pulse operation of the voltage source,    -   applying an external magnetic field perpendicularly or parallel        to the    -   cathode/anode discharge gap,    -   additional operation of a plasma, for example in the form of a        sputter,    -   spark or low-voltage arc plasma,    -   choice of a readily ionizable gas, such as for example Ar, Ne,        He.

Increase of the plasma density by means of a magnetic field is here ofparticular significance, since therewith the probability for ionizationof the gas in the entire plasma space increases. For all conditionsunder which the speed of the charge carriers in the plasma is notparallel to the magnetic field, forces occur which force these chargecarriers onto a circular path. In the relatively small cathode dropregion the movement of the charge carriers is only affected to a minorextent due to the relatively high field strengths. In contrast, themagnetic field has a stronger effect on the positive column. The forcesof the magnetic field decrease the outward diffusion of the chargecarriers and increase the plasma density through the increased impactprobability with the gas molecules.

The plasma booster according to the invention is essentially based onthe effect of the increase of the plasma density through the ignition ofa hollow cathode. If a discharge is operated such that to one anodeseveral cathodes are assigned, the distance of the cathodes from oneanother is of importance. If the distances of the cathodes from oneanother are greater than twice the cathode drop, no mutual effectoccurs. If the cathodes are moved closer to one another or if the plasmadensity is decreased, faster electrons from the one cathode surfaceenter the cathode drop region of the other cathode and therein aredecelerated through the charge, which is also negative, and arereflected. This reflection at the cathode potentials proceeds until theelectron has lost energy, for example through impact. Through thereflection, in turn, the ionization probability is increased. Thecurrent density increases and may increase by a factor of more thanhundred as a function of the type of gas, of the pressure, the distanceor the geometry.

However, at a very small distance of the cathodes with respect to oneanother the current density falls rapidly again, which is explainedtherewith that the current no longer finds its way to the anode out ofthe gap between the two cathodes.

The mutual effect of the cathodes is referred to as hollow cathodeeffect. It is formed if a cathode has hollow spaces which have adiameter smaller the twofold drop space. The size of the cathode dropspace can be strongly affected by the application of a magnetic field.

In conventional plasma treatment installations or electrodeconfigurations the development of hollow cathodes, in particular in thedirect proximity to the surface to be treated, has until now beenavoided as much as possible since, in general, through the formation ofsuch, so-called secondary plasmas highly negative effects result for theplasma treatment process. For example through such discharges energy maybe withdrawn from the plasma, the reactive gas may be too rapidly or toocompletely dissociated or the workpiece surfaces may be overheated, todescribe only some of the disturbing phenomena.

One aim of the present invention, in contrast, is providing a plasmabooster which avoids the disadvantageous effects of a hollow cathode andincreases the plasma density within and outside of the plasma booster tosuch a degree that it contributes to the improvement of the treatmentprocess. The plasma density in the interior is here significantlyhigher, which is of advantage for better dissociation or excitation,respectively, of gaseous precursors.

The principle of the invention will be described by example inconjunction with the following drawing. Therein depict: a plasma boostera workpiece holder a carousel

The plasma booster 1 shown in FIG. 1 is structured of severalsuperjacent circular, elliptical or polygonal annuli 2 or annuli ofcombined geometries, the annuli 2 being disposed at a distance a, whichis sufficiently small to avoid the ignition of a hollow dischargebetween the annuli 2. If the distance is chosen even only slightly toolarge, the ignition of a highly intensive undesired secondary plasmaoccurs between the parallel cathodes 2, with the above describeddisadvantageous consequences.

Distance a between the cathode annuli 2, or distance b between theworkpieces or mountings must consequently be small compared to thetwo-fold cathode drop, advantageously even smaller than the cathodedrop. In the present embodiment a distance a of 1 to 60 mm, preferably 5to 25 mm was chosen.

The total height h of the plasma booster 1 can readily be varied byadding or omitting one or several annuli 2. The annuli 2 can for examplebe held in the desired position by individual connection rods 3 withspacer sleeves not further shown here.

In the case of the present FIG. 1 A, A′, the geometricallycharacteristic parameter is the inner diameter d of the cathode annuliwhich also represents the essential dimension for generating andstabilizing the hollow cathode. In FIG. 1 B the diameter d′of the circleinscribed in the triangle is assumed as the characteristic parameter.The diameter d, d′should therefore be chosen such that the conditionsfor a hollow cathode are satisfied, i.e. smaller or approximately equalto the twofold cathode drop. In the present embodiment a distance d of20 to 200 mm, preferably between 60 to 100 mm was selected. Togetherwith the height h, the diameter d, d′consequently defines the geometryof the hollow cathode, which can not only be implemented in a differentgeometry of the cross section, but also be delimited against theremaining plasma space through different delimitation areas. Forexample, instead of many annular segments 2, only one upper and onelower annular segment may be provided with a grid spanned in between orparallel wires or rods, cylinder or other hollow body with suitableopenings or cut-outs on the circumference, for example in the form ofslots or the like. It is important that there is at least one opening ofthe hollow cathode which keeps open the path of the charge carriers tothe anode.

In the embodiment depicted in FIG. 1 it was further found that coveringof the upper or lower opening by a metal grid 10 can have a positiveeffect on the stability of the plasma.

FIG. 2 shows a workpiece carrier 4 implemented as a plasma booster. Theannuli 5 are provided with receptions 7 for workpieces 8. Thecharacteristic parameter d″ can here be viewed either, as depicted, asthe smallest distance of the workpiece carrier 5 from a carrier rod 6,or as the smallest distance between the spokes 11 of the workpiececarrier, depending on which distance is smaller. It is here alsoessential that the distance a as well as the distances b between theworkpieces 8 is chosen such that no ignition of a hollow cathodedischarge occurs. At least the workpieces of one workpiece carrier planeshould therefore have very similar, or better identical, geometries orthe appropriate distances a or b, respectively, should be set. To attainas uniform a hollow discharge plasma as possible over the height of theplasma booster 4, it is advantageous to provide the spokes 11 of theparticular workpiece carrier annuli 5 in the same position such that, asshown for example in the case depicted in FIG. 2, three identical hollowcathode spaces 12, 12′, 12″ are formed in the interior of the plasmabooster 4.

In principle a single workpiece carrier annulus 5 with a hollow cathodespace 12 or a single annulus 2 can already be applied as a plasmabooster provided the geometry suitable for the correspondingpressure/voltage range is chosen. However, it is understood by a personof skill in the art that appropriate plasma boosters 1 or workpiececarriers 4 implemented as plasma boosters comprised, as depicted in FIG.1 or 2, of several planes of annuli 2 or of workpiece carrier annuli 5achieve a significantly stronger effect. In such plasma boosters 1, 4,for example, reactive gas or precursors for plasma CVD or combinedPVD/CVD processes can highly efficiently be excited or split andconverted into highly reactive species, for example ionized molecules,molecule fragments and/or into radicals. Therewith the deposition rateis also significantly increased and with suitable process management thelayer quality of such plasma CVD layers is improved.

In FIG. 3 is depicted a carousel 9 on which several plasma boosters 1,as shown in FIG. 1, as well as also several workpiece carriers 4, asimplemented in FIG. 2, are disposed. The workpiece carriers 4 cantherein be mounted such that they are rotatably movable and, for exampleas depicted, in cooperation with carousel 9 and receptions 7 bring aboutthe triple rotation of the workpieces 8 in order to achieve a maximallyuniform coating quality. Such a triple rotation is depictedschematically through the corresponding movement arrows 1., 2. and 3. Itis advantageous if the characteristic geometric distance d′of plasmabooster 1 is at least slightly smaller than the characteristic geometricdistance d″ of the workpiece carrier 4, whereby with the application ofa, for example, intermediate-frequency pulse signal according to thePaschen equation, first the plasma in the plasma boosters is ignited.

Such a configuration is especially advantageous if, for example,starting from a metallic adhesion layer, a graduated transition to a DLClayer is to be generated. If the adhesion layer is initially applied ofa pure metal, for example Cr or Ti, and, as is known to the personskilled in the art, other metals of subgroup IV, V or VI of the periodictable of elements or Si or Al can be considered, through a sputter, anarc, a low-voltage arc or another PVD method and subsequently acarbon-containing gas, for example acetylene, methane, ethane, ethyleneor the like are added, a mixed layer is formed essentially containingmetal and metal carbide. However, the formation of sp₃-containing carbonstructures does not or only minimally occur as long as only a DC bias isapplied, since in this case the reactive gas is excited or dissociatedby the plasma at too low an extent. However, if, for example, anintermediate-frequency pulse signal is impressed on the carousel 9, thehollow cathode plasma, due to the smaller distance d, d′ ignites firstin the plasma boosters 1. The ignition is facilitated by each additionalplasma source, for example through the glow discharge of the sputtertargets and, if required, through an additional magnetic field appliedperpendicularly to the hollow cathode plane. This can be generated forexample through a Helmholtz configuration of two magnetic coils in acoating installation.

After the ignition of the hollow cathode plasma in the plasma boosters1, through the increased consumption of the reactive gas, a pressuredrop occurs, which leads to a rapid ignition of a further hollow cathodeplasma in the hollow spaces 12, 12′, 12″ of the workpiece carriers 4 anda further depletion of reactive gas. The ignition of the plasma in theworkpiece carriers 4 takes place through the already high fraction ofcharge carriers from the plasma boosters 1 entirely synchronously andwithout plasma fluctuations. If the reactive gas fraction is increased,which advantageously takes place in the form of a, for example,ramp-like increase of the reactive gas flow, at the surface of thematerials a high fraction of highly excited carbon or hydrocarbon ionsare available which make the buildup of sp³-structures possible.Depending on the process management, now metal-containing sp³-structuresor, for example by back-regulation or screening off the targets,sp³-structures substantially comprised only of carbon and hydrogen canbe deposited. A further advantage is obtained when using such plasmaboosters 1 or workpiece carriers 4 thereby that the process can bemanaged such that even in the deposition of insulating, for example DLClayers, on workpieces, the conductivity on the inside of the plasmabooster 1 or of the workpiece carrier 4, is retained. This results dueto temperature loading increased in this region or due to the increasedbombardment with ionized particles, which causes graphitization on theinner surface of the hollow body or of the hollow cathode when using,for example, a carbon-containing reactive gas.

In the following in conjunction with examples, the distinction fromprior art and the advantageous effect of the employment of plasmaboosters according to the invention will be demonstrated. Detailsregarding the process parameters and geometric implementation of thearrangement can be found in Table 1. The process was carried out on acarousel with 6 or 12 trees.

EXAMPLE 1

Here the workpieces are charged according to prior art onto trees suchthat a hollow cathode is avoided. The substrate current in the processis low, the coating rate is low.

EXAMPLE 2

Here the pieces are charged onto trees which correspond to anarrangement according to the invention. When an IF bias is impressed ahollow cathode is thereby ignited and an increase of the substratecurrent as well as an increased deposition rate compared to Example 1.The geometric parameters of the hollow discharge were so adapted to theprocess parameters that the pieces were neither overheated nor the layerquality negatively affected.

EXAMPLE 3

Here the workpieces were charged as in Example 1, additionally, two of12 trees were replaced with an arrangement described as in FIG. 1.Alternatively, on one carousel loaded with 6 trees, additionally, 3plasma boosters 1 as in FIG. 3 were utilized. In both cases a positiveeffect on the deposition rate was observed.

EXAMPLE 4

Here the pieces were charged onto an arrangement as in Example 2, thehollow cathode is operated at a higher pressure, which leads to anadditional increase of the substrate current and of the deposition ratecompared to example 1 and 2. Under these conditions the pieces were alsoneither overheated nor the layer quality negatively affected.

EXAMPLE 5

Here the distances were greater than in Example 1, however, smaller thanin Example 2. Clearly, d″ here corresponds to a mean distance in therange of a maximal electron reflection, since here the hollow cathodeburns very intensively, the pieces are overheated and a poor layerquality is generated through the graphitization.

EXAMPLE 6

Shows a marked dependence of the effect of the plasma booster on thefrequency of the impressed electric signal. With a frequency increase of50 to 100 kHz, at otherwise constant parameters, a significant increase,compared to Example 4, of the substrate current and of the coating ratecould be achieved.

Although in the preceding many different feasibilities for carrying outthe invention were described, it is evident to a person of skill in theart by means of the description that there are still a large number ofother feasibilities for realizing corresponding arrangements forignition or boosting the plasma. For example a corresponding arrangementcan also be disposed on the vacuum chamber, the chamber bottom orchamber cover instead of on the carousel provided the arrangement isinsulated from the receptacle and a corresponding electric signal, forexample the substrate bias signal, is impressed. TABLE 1 Examples of theInvention Example 3: Example 2: Setup with additional Example 1: Setupwith triply rotating arrangements without Prior Art parts on thearrangement loading Reactive gas flow 20-320 sccm 220-350 sccm 220-350sccm Working pressure 5.0-7.0 10⁻³ mbar 5.0-7.0 10⁻³ mbar 5.0-7.0 10⁻³mbar Distance d″ workpiece to 10 mm 60-100 mm 10 mm mounting surfaceLoading condition plate workpiece, as well triple rotation; 40 plateworkpiece, as well as triple rotation: 10 workpieces on one plate astriple rotation, as in workpieces on one plate Example 1 Number of trees12 6 6 Amplitude voltage −800-1000 V −800-1000 V −800-1000 V Substratecurrent 0.5-1.5 A 1.5-4.0 A 1.5-4.0 A Signal frequency 50 kHz 50 kHz 50kHz Deposition rate 0.2 μm/h 0.9 μm/h 0.9 μm/h Part temperature 200° C.200° C. 200-250° C. Example 5: Example 4: Setup on arrangement Example6: Setup with triply rotating with distances that are Setup with triplyrotating parts on the arrangement too small parts on the arrangementReactive gas flow 350-500 sccm 220-350 sccm 350-500 sccm Workingpressure 7.0-1.2 10⁻² mbar 4.5-7.0 10⁻³ mbar 7.0-1.2 10⁻² mbar Distanced″ workpiece to 60-100 mm 40 mm 60-100 mm mounting surface Loadingcondition triple rotation; 30 triple rotation; 30 triple rotation; 30workpieces on one plate workpieces on one plate workpieces on one plateNumber of trees 12 12 6 Amplitude voltage −800-1000 V −800-1000 V−800-1000 V Substrate current 2.0-6.0 A 2.0-20 A unstable 4.0-12 ASignal frequency 50 kHz 50 kHz 100 kHz Deposition rate 1.5 μm/h —2.0-2.5 μm/h Part temperature >250° C. >250° C. −250° C.

1. Arrangement for boosting and/or igniting a glow discharge plasma forthe treatment, in particular for the coating, of workpieces, with atleast one hollow body of an electrically conductive material, whereinthe hollow space of the hollow body is formed such that when an electricsignal is applied to the hollow body at least in a certain pressure andvoltage range the geometric conditions for the ignition of a dischargein the interior of the hollow body are satisfied, and the hollow bodycomprises at least one opening through which charge carriers can flowoff into the environs of the arrangement in order to make here possiblethe ignition and operation of a plasma or to boost a plasma existinghere, characterized in that the arrangement comprises means whichconnect the hollow body electrically with the workpieces such that thehollow body is essentially at workpiece potential.
 2. Arrangement asclaimed in claim 1, characterized in that the hollow body is fastened ona carousel (9) for the reception of workpiece carriers (4). 3.Arrangement as claimed in claim 1, characterized in that the geometricconditions are satisfied for a pressure range between 1×10⁻³ to 5×10⁻²mbar, preferably between 4×10⁻³ to 2×10⁻² mbar.
 4. Arrangement asclaimed in claim 1, characterized in that the geometric conditions foran electric signal are satisfied with a voltage range between 200 to2000 V, preferably between 400 to 1200 V.
 5. Arrangement as claimed inclaim 3, characterized in that the electric signal is a DC voltage, anAC voltage, in particular a bipolar or unipolar pulsed AC voltage signalin the intermediate frequency range.
 6. Arrangement as claimed in claim1, characterized in that the hollow body has a height h and a crosssection with at least one geometrically characteristic parameter d,wherein the cross section has the form of a circle, an ellipse of apolygon or a form composed of different geometries, and the hollow bodyhas at least one lateral face extending over the height h. 7.Arrangement as claimed in claim 6, characterized in that the hollow bodyis covered at the top and/or bottom with a grid.
 8. Arrangement asclaimed in claim 6, characterized in that the lateral face of the hollowbody has several openings or slots over its height h.
 9. Arrangement asclaimed in claim 6, characterized in that the at least one lateral faceof the hollow body comprises grids or parallel wires or rods, oressentially consists of a grid or parallel wires or rods. 10.Arrangement as claimed in claim 6, characterized in that the hollow bodycomprises several circular, elliptical, polygonal annuli or annuli ofcombined geometries, disposed one above the other, wherein the annuliare disposed at a distance a, which is sufficiently small to avoid theignition of a hollow discharge between the annuli.
 11. Arrangement asclaimed in claim 10, characterized in that the distance a is smallerthan the cathode drop in a certain pressure and voltage range, inparticular is between 1 to 60 mm, preferably between 5 to 25 mm. 12.Arrangement as claimed in claim 10, characterized in that the annuli areformed as workpiece holders with receptions (7), wherein the receptions(7) or the workpieces (8) are disposed with respect to one another at adistance b, which is sufficiently small to avoid the ignition of ahollow discharge between the workpiece receptions (7) or the workpieces(8).
 13. Arrangement as claimed in claim 12, characterized in thatdistance a and/or b is smaller than the cathode drop in a certainpressure and voltage range, in particular is between 1 to 60 mm,preferably between 5 to 25 mm.
 14. Arrangement as claimed in claim 6,characterized in that distance d is less or equal to the twofold,however greater or equal to the simple cathode drop in a certainpressure and voltage range, in particular is between 20 to 200 mm,preferably between 60 and 100 mm.
 15. Vacuum treatment installation forplasma treatment, in particular for the plasma coating of workpiecescharacterized thereby that it comprises an arrangement according toclaim
 1. 16. Vacuum treatment installation as claimed in claim 14,characterized in that the installation comprises an additional magneticfield generating device, which acts onto the hollow cathode dischargegap or boosts the plasma.
 17. Vacuum treatment installation as claimedin claim 16, characterized in that through the magnetic field generatingdevice a magnetic field 13 is producible, that acts perpendicularly ontothe hollow cathode discharge gap.
 18. Vacuum treatment method,characterized in that an arrangement according to claim 14 for theignition and maintaining in operation of a plasma or for boosting analready existing plasma is utilized.
 19. Vacuum treatment method asclaimed in claim 18, characterized in that the arrangement is utilizedin order to excite or split reactive gas or precursors for a plasma CVDprocess or for a combined PVD/CVD process.